1. Field of the Invention
This application is directed to masks for improving the depth of focus of an eye of a human patient and methods and apparatuses for applying such masks. More particularly, this application is directed to apparatuses and methods for aligning a mask with the line of sight of an eye and applying the mask to the eye.
2. Description of the Related Art
Presbyopia, or the inability to clearly see objects up close is a common condition that afflicts many adults over the age of 40. Presbyopia diminishes the ability to see or read up close. Near objects appear blurry and out of focus. Presbyopia may be caused by defects in the focusing elements of the eye or the inability (due to aging) of the ciliary muscles to contract and relax and thereby control the shape of the lens in the eye.
The human eye functions by receiving light rays from an object and bending, refracting, and focusing those rays. The primary focusing elements of the human eye are the lens (also referred to as the intraocular lens) and the cornea. Light rays from an object are bent by the cornea, which is located in the anterior part of the eye. The light rays subsequently pass through the intraocular lens and are focused thereby onto the retina, which is the primary light receiving element of the eye. From the retina, the light rays are converted to electrical impulses which are then transmitted by the optic nerves to the brain.
Ideally, the cornea and lens bend and focus the light rays in such a way that they converge at a single point on the retina. Convergence of the light rays on the retina produces a focused image. However, if the cornea or the lens are not functioning properly, or are irregularly shaped, the images may not converge at a single point on the retina. Similarly, the image may not converge at a single point on the retina if the muscles in the eye can no longer adequately control the lens. This condition is sometimes described as loss of accommodation. In presbyopic patients, for example, the light rays often converge at a point behind the retina. To the patient, the resulting image is out of focus and appears blurry.
Traditionally, vision improvement has been achieved by prescribing eye glasses or contact lenses to the patient. Eye glasses and contact lenses are shaped and curved to help bend light rays and improve focusing of the light rays onto the retina of the patient. However, some vision deficiencies, such as presbyopia, are not adequately addressed by these approaches.